\section{Components Used}
\label{components_used}

This section provides information about specific solutions and
workarounds used in PaWS application.

\begin{itemize}

  \item {\bf Creating graphics} 
  
    Functional requirement No. \ref{req:dependence_graphs} specifies
    that PaWS must be able to create and present dependence graphs. To
    create them in \emph{dot} \cite{dot_format} format\footnote{The
      DOT language is a description language for describing graphs in
      a human and machine readable format.} a PIPS mechanism is used
    (shown in the listing \ref{DotDependenceGraphPrinting}).
  
  \lstset{language=Python,caption={Dependence graph in dot format printing},label=DotDependenceGraphPrinting}
  \begin{lstlisting}
function.print_dot_dependence_graph()
  \end{lstlisting}
  
  A file in \emph{dot} format is transformed into an image in
  \emph{png} format by command \emph{dot} of GraphViz
  Software\cite{graphviz}. Details can be found in \emph{dot} user
  manual: \url{http://www.graphviz.org/pdf/dot.1.pdf}.
  
  \item {\bf Presenting graphics} 
  
    To present dependence graphs, the jQZoom Evolution\cite{jqzoom}
    library is used. This is a light plugin based on JQuery, described
    in \ref{web_application_technologies}. It allows to present the
    image in more user-friendly way. There is small
    thumbnail\footnote{Thumbnail is the small illustration which
      represents the original image at a much smaller size.} shown and
    hoovering mouse over it enables zooming preview of selected part
    of the original, the large image. Moreover this plugin is very easy
    to use, due to its usage of JQuery, and to integrate with PaWS.
  
    The only potential problem of jQZoom usage is the need to provide
    two copies of the image in two sizes: big and thumbnail. To
    fulfill this requirement the Python Image Library (PIL) \cite{pil}
    is used. This is a Python module, which provides all the operations
    dedicated to images processing and supports many files formats. It
    is written in Python and hence is very easy to integrate in the PaWS
    framework. This is its main advantage.
  
  \item {\bf Uploading files}
  
    According to the functional requirement
    No. \ref{req:uploading_files}, PaWS enables user to browse and
    pick his/her own files. Uploading user files caused two problems:

  \begin{itemize}

  \item HTML ``input'' with \emph{type=``file''} used for uploading
    files is not customizable. That means that it is impossible to
    change the style of the button and file name label, which is
    causing aesthetic conflict with the rest of the HTML site.

  \item Uploading files through AJAX requests is impossible because of
    the browsers restrictions and the XmlHttpRequest object
    limitations\cite{ajax_files_upload}. At the same time, PaWS needs
    to be able to upload user files without refreshing the site. Since the
    stardard HTML solution is causing site refreshing, this requires
    the usage of AJAX.

  \end{itemize}
  
  The first problem is easy to solve by creating transparent files
  upload panel which covers false, styled panel (button and file name
  label). Due to that solution, only well styled button and label are
  visible but they are not active - invisible layer of not properly
  styled files upload panel captures users activity.
  
  The second problem is more serious, but it has also been solved. There
  is a hidden, also transparent and invisible, IFrame used as a target
  for file uploading (``target'' attribute is used). When a form with
  the file upload is submitted, the result will be present in a hidden,
  refreshed IFrame, but it can not be seen by user. Content of this
  frame is copied to its proper destination, the visible window. The last
  step is very easy and can be done without refreshing the whole page.
  
  \item {\bf Loading multiple files}
  
    The same requirement No. \ref{req:uploading_files} results in the
    possibility to load several user files packed in one archive file,
    using ``zip'' extension. The only restriction is that all files
    must be written in the same programming language. It is due to
    PyPS framework current limitations.
  
    Python module \emph{zipfile}\cite{zipfile} is used to handle this
    case. It provides archive creating, reading, writing and listing.
  
    For each file, a new tab is created and, when performing an
    operation, the user has to choose one specific function to
    analyse/transform. Dependence graphs are created for all functions
    from all the files.
  
  \item {\bf Printing Result Files}
  
    Functional requirement No.~\ref{req:printing_results} requests the
    possibility of printing the results of the PIPS analyses and
    transformations. To print only the results, not a whole WEB page,
    a special hidden, user invisible frame is used. At user request,
    computation result is loaded into the invisible frame which is
    printed.
  
    There is another possible solution for printing only part of a WEB
    page - usage of special style class which defines which parts of
    the site should be visible when the page is printed. The disadvantage
    of this approach is that it prints all of the page, even if a large
    part of it is invisible, which causes a large wasting of the
    space.
  
  \item {\bf Language detection}
  
    Functional requirement No. \ref{req:language_detection} refers to
    the language detection. It is based on simple tokens
    recognition. It can distinguish between C and Fortran only.
  %% In addition, distinction between different versions of Fortran language (77 and 95) needs compilation.

  %% TO ADD: mechanism! Event when typing source code, pre-compilation
  
  \item {\bf Deleting temporary files}
  
    Most temporary files created during PaWS operations are deleted
    immediately after use. Unfortunately, there are also files which
    need to be kept on the server for a longer time. This applies to
    the files which are used to present results to user, graphs images
    or files with result of transformations and analysis for
    download. To preserve disk space on the server side, requirement
    No. \ref{req:deleting_files}, a cron\footnote{It is a customizable
      Linux job scheduler, which runs periodically user scripts or
      commands\cite{cron}.} task is used. Every hour, a Python script,
    \emph{pawsd.py}, located in \emph{pawsapp$\backslash$utils}
    directory, is invoked to delete all temporary files older than 2
    hours.
  
\end{itemize}